As a material for next-generation power semiconductor devices, a group-III nitride, for example, a GaN (gallium nitride)-based semiconductor has been expected. The GaN-based semiconductor has a large bandgap in comparison with Si (silicon). For this reason, in comparison with an Si (silicon) semiconductor device, by using a GaN-based semiconductor device, a power semiconductor device with a small size and a high breakdown voltage can be implemented. In addition, accordingly, a parasitic capacitance can be reduced, and thus, a power semiconductor device with high-speed driving can be implemented.
Generally, a high electron mobility transistor (HEMT) structure using a two-dimensional electron gas (2DEG) as carriers is applied to a GaN-based transistor. A typical HEMT is a normally-on transistor which becomes conductive even when no voltage is applied to the gate. For this reason, there is a problem in that it is difficult to implement a normally-off transistor which does not become conductive if no voltage is applied to the gate.
In such a power supply circuit for dealing with a large power of several hundred volts to one thousand volts, the normally-off operation is required in terms of emphasis on safety. Therefore, a circuit configuration for implementing the normally-off operation by performing a cascode connection of connecting a normally-on GaN-based transistor and a normally-off Si transistor has been proposed.
In addition, in the case of a circuit configuration where a main circuit current flowing between the drain and the source and a driving current flowing between the gate and the source share a source inductance, due to the electromotive force generated in the source inductance with a time change of the main circuit current, a driving current is also modulated. As problems generated along with this, there is a problem of delay such as reduction in a rising speed or a falling speed of a power semiconductor device or a problem of ringing as a rapid time change of the drain current and the source voltage. Therefore, a circuit configuration using Kelvin connection where the main circuit current and the gate driving current do not share the source inductance has been proposed.